Conventionally, infrared microscopes as means for obtaining optical information of microscopic parts on samples are known. For example, to investigate molecular structures of organic substances attached to a surface of an individual, infrared microscopes irradiate infrared light to a microscopic part on a sample held by a stage and detect transmitted or reflected infrared light by a detector to measure absorption spectrum and the like.
Recently, measurement methods which irradiate linear infrared light to a sample (linear irradiation) to obtain spectra of a plurality of points from the elongated irradiated region are used. These methods shorten measurement time compared to measurement methods which uses general spot irradiation. In measurement performed by linear irradiation, generally, an array detector is used to detect spectra of a plurality of point. However, crosstalk, which spectra overlap each other, cannot be avoided, and sufficient spatial resolution cannot be obtained. Patent Literature 1 discloses an art to eliminate crosstalk (overlapping of spectra) by irradiating a linear infrared light to a sample and making spaces bigger between light-receiving elements in a light-receiving element surface of a detector for detecting the infrared light transmitted through or effected by the sample.